The present invention relates to a device for purifying the exhaust gas of an internal combustion engine.
The exhaust gas of an internal combustion engine and, particularly, of a diesel engine, contains particulates comprising carbon as a chief component. Particulates are harmful materials and thus it has been suggested that a particulate filter should be arranged in the exhaust system to trap particulates before they are emitted into the atmosphere. In such a particulate filter, the trapped particulates must be burned and removed to prevent resistance to the exhaust gas from increasing due to the blocked meshes.
In such a regeneration of the particulate filter, if the temperature of the particulates becomes about 600 degrees C., they ignite and burn. However, usually, the temperature of an exhaust gas of a diesel engine is considerably lower than 600 degrees C. and thus a heating means is required to heat the particulate filter itself.
Japanese Examined Patent Publication No. 7-106290 discloses that if one of the platinum group metals and one of the oxides of an alkali earth metal are carried on the filter, the particulates on the filter burn and are removed successively at about 400 degrees C. 400 degrees C. is a typical temperature of the exhaust gas of a diesel engine.
However, when the above-mentioned filter is used, the temperature of the exhaust gas is not always about 400 degrees C. Further, a large amount of particulates can be discharged from the engine according to an engine operating condition. Thus, particulates that cannot be burned and removed each time can deposit on the filter.
In this filter, if a certain amount of particulates deposits on the filter, the ability to burn and remove particulates drops so much that the filter cannot be regenerated by itself. Thus, if such a filter is merely arranged in the exhaust system, the blocking of the filter meshes can occur relative quickly and thus the engine output can drop.
Therefore, an object of the present invention is to provide a device, for purifying the exhaust gas of an internal combustion engine, which can oxidize and remove the trapped particulates on the particulate filter and can prevent blocking of the particulate filter meshes.
According to the present invention, there is provided a device for purifying the exhaust gas of an internal combustion engine comprising a particulate filter arranged in the exhaust system and a reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the trapped particulates are oxidized on the particulate filter, the particulate filter has a trapping wall for trapping the particulates, the trapping wall has a first trapping surface and a second trapping surface, and the reversing means reverses the exhaust gas upstream side and the downstream side of the particulate filter so that the first trapping surface and the second trapping surface are used alternately to trap the particulates.
Further, according to the present invention, there is provided another device for purifying the exhaust gas of an internal combustion engine comprising a particulate filter arranged in the exhaust system and a reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the particulate filter carries an active-oxygen releasing agent, active-oxygen released from the active-oxygen releasing agent oxidizes the trapped particulates on the particulate filter, the active-oxygen releasing agent holds NOx to combine the NOx with oxygen when excessive oxygen is present in the surroundings and releases to decompose the combined NOx and oxygen into NOx and active-oxygen when the oxygen concentration in the surroundings drops, the particulate filter has a trapping wall for trapping the particulates, the trapping wall has a first trapping surface and a second trapping surface, the reversing means reverses the exhaust gas upstream side and the downstream side of the particulate filter so that the first trapping surface and the second trapping surface are used alternately to trap the particulates, and the oxygen concentration in the surroundings is sometimes made to drop.